Under the forces of wind, electrical transmission lines such as telephone cables, power lines and the like can bounce in a vertical fashion known as "galloping". The galloping poses a threat to the support of the line, and the line may become tangled with neighboring lines. There are three primary categories of galloping motion in long span catenary cables, wires and conductors. The first is exhibited by a round cable that is supported by towers spaced apart at intervals of several hundred feet. Under certain weather conditions, ice tends to form along the length of the cable into the direction of the wind. As a result, the ice forms a wing protruding out of the cable. When the wind catches the aerodynamic shape of the iced cable, a vertical lift is generated and results in galloping. Hence, there is galloping due to wind force acting on the aerodynamics of an iced cable.
The second category of galloping is exhibited by out-of-round shaped lines which when twisted by wind have an aerodynamic profile without any added ice formation. One such line is a telephone cable which has a uniform figure eight cross section. When the wind blows, the figure eight shape is turned to one side and forms in effect a wing enabling air lift which results in galloping.
The third category is exhibited by steeply angled cables that cut into the wind. The vertical lift that results in galloping is due to the angle that is formed between the wind and the cable. One example of such a cable is a guy wire.
In all three cases the cable is subject to gallop or vertical dancing motion of large amplitude if the wind force and its angle with the aerodynamics of the cable are related in a way that overcomes the inherent friction of the cable and its supports. In order to counteract a tendency toward galloping once the conditions of wind force and complementary angle are present, the damping or friction of the cable must be increased or the aerodynamics of the cable must be changed.
Most methods for increasing the damping in a transmission line or cable apply the long recognized principle that a twisted shape will not gallop. In the case of ice formed about a cable the fundamental idea behind twisting the cable so as to increase aerodynamic damping is "to confuse the ice shape" as it is distributed in a span which would otherwise gallop if the ice shape were uniform. Only a few degrees of twist may be required to prevent galloping of the span. This principle has been successfully applied in twisted telephone cables to form a figure eight shape in its cross section which continually varies along the span and thus breaks uniformity in the ice formation along the length of the cable. More recently, the same process of twisting two conductors upon each other forming a varying figure eight cross section has been applied to overhead power conductors such as in the twisted T-2 Conductor by the Kaiser Aluminum & Chemical Company in the U.S.
The same methodology is employed in the add-on unit of Preformed Line Produts, Inc., called "The Spoiler". The add-on unit is wrapped around the conductor over 30% of the span and thereby adds discontinuity to the ice formation along the conductor span.
Another method for increasing damping is the addition of a "drag damper" over 30% of the length of the span. The "drag damper" is in the shape of a small flat plate which enhances the drag force and thereby reduces the angle at which the wind acts upon an iced cable. In another type of drag damper called the "Windamper" (a registered trademark of Albert Richardson) the devide is attached to a single point in the conductor span below the conductor. The device blows with the wind and twists the conductor itself to create a non-uniform distribution of ice shape along the span.
In the case of TV antenna guy cables, there is another method that has come into widespread use. Again, based on the fundamental principle of increased damping or friction, a device called the "Sandamper" (a registered trademark of Albert Richardson) prevents galloping of TV guy cables by a ball half filled with sand rolling on top of a portion of the cable, counteracting the vertical lift of the cable.